Gelifluction, thixotropy and yield stress were measured from <5 g soil samples taken from Signy, Alectoria, Greenwich, Wiencke and Livingston islands in the maritime Antarctic using a temperature-controlled rotational rheometer. The small sample size that this method permitted is compatible with sampling from sensitive sample locations. An oscillating 10 Pa shear stress was applied to samples at -0.5 kPa water potential. Two freeze-thaw cycles had temperature ramps from 5°C to -10°C over 2 h, followed by -10°C to 5°C over 2 h and finally at 5°C for 1 h. At freezing onset, the shear modulus, G, dropped to 4-50 per cent of thawed G, with no differences between locations. At thawing onset, G dropped to 8-32 per cent of thawed G, with significant differences between locations (P <0.001). Thixotropy was then measured by applying a 2 kPa oscillating shear stress for 10 min, followed by relaxation at 10 Pa for 2 h. The increased shear stress caused G to drop to less than 8 per cent of the pre-stressed value, with no difference between locations. After 0.1 and 2 h, G was 18-65 per cent and 31-82 per cent of the pre-stressed value, respectively. A shear ramp determined yield stresses ranging from 494-2217 Pa. These findings demonstrate the potential risk of more frequent freeze-thaw cycles or the occurrence of thawed soil to the stability of polar soils. Gelifluction through more frequent freeze-thaw cycles could result in increased slope movement, whereas thixotropy caused by trampling of thawed soils could exacerbate mechanical damage of surface soils.
Funding was supplied by the UK Natural Environment Research Council through the Antarctic Funding Initiative (AFI 7/05; NE/D00893X/1). Logistical support was provided by the British Antarctic Survey’ s Operations Group and the Royal Navy (HMS Endurance). We thank Peter Fretwell of the British Antarctic Survey for drawing Figure 1. We are grateful to the China Scholarship Council which supported Dr Benhua Sun through a Special Western Project, for support from 111 Project No. 12007. The work was carried out at the Scottish Crop Research Institute, which received funding from the Scottish Government.
- Maritime Antarctic
- Rotational rheometer
- Yield stress